There are various types of elevator systems. Some are traction-based and include roping connecting an elevator car to a counterweight. A machine causes a traction sheave to rotate to cause longitudinal movement of the roping for moving the elevator car up or down. Other elevator systems are hydraulic based and include a plunger or jack that extends or retracts based on hydraulic fluid supplied into or withdrawn from the plunger. As the plunger extends, the elevator car moves upward and as the plunger retracts, the elevator car moves downward.
Regardless of the type of elevator system, measures are taken to protect mechanics and technicians performing maintenance on the elevator system. In the case of hydraulic elevators, a safety or shutoff valve prevents the hydraulic fluid from leaving the plunger so that the elevator car cannot descend. Known shutoff valves are manually operated and typically include a handle that provides a visual confirmation of the position of the valve, such as open or closed.
Modern trends in elevator systems include eliminating machine rooms and making the elevator system integration into a building as seamless as possible. These changes are beneficial to building owners but present challenges to elevator system providers. For example, the shutoff valve for a hydraulic elevator system may be located in a machine room or a cabinet near the elevator hoistway. Eliminating such machine rooms and cabinets makes it challenging to incorporate a shutoff valve to provide the desired protection against elevator car movement during maintenance procedures when an individual may be located beneath the car.
While an electrically operated, remotely controllable valve could potentially be used in such systems, there are a few drawbacks to that approach. Otis Elevator Company, for example, prefers a visual indication of the position of a manual shutoff valve. Many electrically operated valves have internally moving parts and do not provide external, visual indications of valve position. Additionally, an electrically operated valve would introduce additional expense compared to a manually operated valve. Further, an electrically operated valve would require sufficient power and would not be useful in situations where power is lost or not available.
There is a need for a valve arrangement for selectively controlling whether an elevator car can move in a hydraulic elevator system even in installations where a manually actuated valve is not accessible.